This is more recent, but the story behind Rafe's dead fiancee, Emily. It was mentioned and used for the silly story of Meredith holding him captive, but never really explained. Which is part of what makes Rafe such a poorly drawn character IMO. His history has never been filled in. We don't know where he's been, where he's lived, what he's been through, what really happened on that wedding day to Emily. We don't know where he's coming from, what life he's led before the safehouse. GG's got plenty of faults but that isn't his fault. There's just no there there with Rafe and there never has been, and that's on the writers.